Open Trillian. If you haven’t already added an AIM account, click the "Trillian" menu button and select "Manage Accounts." Click the "Add a New Account" button and click "AOL Instant Messenger" on the submenu. Type your AIM account credentials in the displayed fields and click "Connect."

Click the "Trillian" menu button and click "Add Contact." Click the "Account" drop-down menu and select your AIM screenname. For the "Username" field, type "+" followed by the full phone number of the person you want to text. Do not use any spaces after the "plus sign" or between any parts of the number itself. Click "Add" to add the phone number to your AIM contacts list.

Double-click the phone number in the Trillian contacts list. Type your text message in the box in the lower part of the chat window and then press "Enter." When your contact receives the text, he can reply to the SMS to send further responses, and any replies will appear in your chat window. Type a message and press "Enter" to send additional text messages to the recipient.